Loans and Allowance for Loan Losses - Schedule of Non-Accrual Loans (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	$ 23,565	$ 27,926	$ 26,297
Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	109	131	286
Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	19,027	22,548	24,059
Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	3,640	4,281	1,366
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Non-accrual loans	$ 789	$ 966	$ 586